Synthesis and reactivity of a stable η2-(diphosphirenylium)(W(CO)5 complex

Full text of DOI:10.1021/ja971973a

J. Am. Chem. Soc. 1997, 119, 9923-9924
9923
Scheme 1
Synthesis and Reactivity of a Stable
η2-(Diphosphirenylium)W(CO)5 Complex
Didier Bourissou, Yves Canac, Maria Isabel Collado,
Antoine Baceiredo, and Guy Bertrand*
Laboratoire de Chimie de Coordination du CNRS
205, route de Narbonne, 31077
Scheme 2
Toulouse Ce´dex 04, France
ReceiVed June 16, 1997
Several cyclopropenium salts A (Scheme 1), the prototype
for 2-π-electron Hu¨ckel aromatic systems, have been prepared
over the last 40 years.1 According to calculations,2 the azirinyl
cations B exhibit a less-pronounced aromatic character due to
the π-polarization toward nitrogen; to date, these compounds
remain unknown. Replacement of the nitrogen atom by a
phosphorus center should decrease the ring strain and allow
better delocalization of the (2π) electrons. However, phos-
phirenyl cations C have been observed spectroscopically only
in SO2 solution at -78 °C,3 or when complexed in an η3-fashion
to an electron-rich Ni0 center.4 In the series of cationic 2-π-
electron three-membered rings, no derivatives featuring two
heteroatoms are known; even the postulated involvement5 of
the diazirinyl cation D in the exchange reaction of nucleophiles
with halodiazirines has been refuted.6 Here, we report the
synthesis and reactivity of the first stable diphosphirenylium
salt E bound in an η2-manner to a transition metal center.
It is well-known that amino substituents and transition metal
centers dramatically stabilize electron-deficient species1c,7 and
low-coordinate phosphorus compounds,8 respectively. More-
over, it has been clearly established that coordinated phosphe-
nium salts can be easily obtained by heterolytic cleavage of
the P-X bond of halogenophosphine complexes.9 Therefore,
1-halogeno-3-aminodiphosphirene complexes10 seemed to be
ideal precursors for the desired diphosphirenylium salts. Treat-
ment of the 1H-diphosphirene 111 with 1 equiv of W(CO)5(THF)
at low temperature in THF readily affords complex 2 as a yellow
oil, in 65% yield.12 The spectroscopic data observed for 2 are
comparable to those described for analogous compounds
prepared by other routes.10b,c Reaction of 2 with 2 equiv of
hydrogen chloride in pentane13 gives 1-chloro-1H-diphosphirene
(3) as a yellow oil in 69% yield12 (Scheme 2). The substitution
of the amino group at the λ3-phosphorus atom is clearly evident
from mass spectrometry (CI, CH4, m/z ) 534) and from the
NMR spectra (data observed for 2 and 3 are similar). Interest-
ingly, the mass spectrum features fragment peaks which
correspond to both complexed and uncomplexed diphosphirenyl
cations {m/z ) 498 (M - Cl)+ and 174 [M - Cl - W(CO)5]+}.
Treatment of 3 with sodium tetraphenylborate in dichlo-
romethane at room temperature affords the P-phenyl-1H-
diphosphirene 412 (Scheme 2). The replacement of the chlorine
atom by a phenyl group at the λ3-phosphorus center is again
apparent from the mass spectrum (CI, NH3, m/z ) 576) and
the 31P NMR spectra [-177.5, dt, J(P-P) ) 148.4 Hz, J(P-
H) ) 13.2 Hz, λ3-P]. The formation of 4 probably results from
the ionization of the P-Cl bond of 3 leading to a transient
diphosphirenylium, which abstracts a phenyl group from the
tetraphenylborate counterion. In order to prevent nucleophile
(1) (a) Breslow, R.; Yuan, C. J. Am. Chem. Soc. 1958, 80, 5991. (b)
Breslow, R.; Ho¨ver, H.; Chang, H. W. J. Am. Chem. Soc. 1962, 84, 3168.
(c) Yoshida, Z. Top. Curr. Chem. 1973, 40, 47. (d) Komatsu, K.; Tomioka,
J.; Okamoto, K. Tetrahedron Lett. 1980, 21, 947. (e) Moss, R. A.; Munjal,
R. C. Tetrahedron Lett. 1980, 21, 1221. (f) Takeuchi, K.; Kitagawa, T.;
Miyabu, A.; Hori, H.; Komatsu, K. J. Org. Chem. 1993, 58, 5802. (g)
Minkin, V. I.; Glukhovtsev, M. N.; Simkin, B. Ya. Aromaticity and Anti-
aromaticity: Electronic and Structural Aspects, Wiley: New York, 1994;
pp 177-183.
(2) Byun, Y.-G.; Saebo, S.; Pittman, C. U., Jr. J. Am. Chem. Soc. 1991,
113, 3689.
(3) Laali, K. K.; Geissler, B.; Wagner, O.; Hoffmann, J.; Armbrust, R.;
Eisfeld, W.; Regitz, M. J. Am. Chem. Soc. 1994, 116, 9407.
(4) Avent, A. G.; Geoffrey, F.; Cloke, N.; Flower, K. R.; Hitchcock, P.
B.; Nixon, J. F.; Vickers, D. M. Angew. Chem., Int. Ed. Engl. 1994, 33,
2330.
(5) (a) Graham, W. H. J. Am. Chem. Soc. 1965, 87, 4396. (b) Krogh-
Jespersen, K.; Young, C. M.; Moss, R. A.; Wostowski, M. Tetrahedron
Lett. 1982, 23, 2339. (c) Moss, R. A.; Terpinski, J.; Cox, D. P.; Denney,
D. Z.; Krogh-Jespersen, K. J. Am. Chem. Soc. 1985, 107, 2743. (d) Liu,
M. T. H.; Paike, N. Tetrahedron Lett. 1987, 28, 3763. (e) Liu, M. T. H.;
Doyle, M. P.; Loh, K.-L.; Anand, S. M. J. Org. Chem. 1987, 52, 323. (f)
Moss, R. A. Acc. Chem. Res. 1989, 22, 15.
(6) (a) Dailey, W. P. Tetrahedron Lett. 1987, 28, 5801. (b) Bainbridge,
K. E.; Dailey, W. P. Tetrahedron Lett. 1989, 30, 4901. (c) Creary, X.; Sky,
A. F. J. Am. Chem. Soc. 1990, 112, 368. (d) Creary, X. Acc. Chem. Res.
1992, 25, 31.
(7) (a) Cowley, A. H.; Cushner, M. C.; Szobota, J. S. J. Am. Chem. Soc.
1978, 100, 7784. (b) Atkinson, R. S. In Azides and Nitrenes: ReactiVity
and Utility; Shriven, E. F. V., Ed.; Academic Press: New York, 1984; pp
258-285. (c) Alder, R. W.; Allen, P. R.; Murray, M.; Orpen, A. G. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1121. (d) Boche, G.; Andrews, P.; Harms,
K.; Marsch, M.; Rangappa, K. S.; Schimeczek, M.; Willeke, C. J. Am. Chem.
Soc. 1996, 118, 4925.
(8) Regitz, M.; Scherer, O. J. Multiple Bonds and Low Coordination in
Phosphorus Chemistry; Georg Thieme Verlag: Stuttgart, 1990.
(9) (a) Montemayor, R. G.; Sauer, D. T.; Fleming, S.; Bennett, D. W.;
Thomas, M. G.; Parry, R. W. J. Am. Chem. Soc. 1978, 100, 2231. (b)
Cowley, A. H.; Kemp, R. A.; Wilburn, J. C. Inorg. Chem. 1981, 20, 4289.
(10) Three examples of 1H-diphosphirenes have been reported so far:
(a) Niecke, E.; Streubel, R.; Nieger, M.; Stalke, D. Angew. Chem., Int. Ed.
Engl. 1989, 28, 1673. (b) Mercier, F.; Ricard, L.; Mathey, F.; Regitz, M. J.
Chem. Soc., Chem. Commun. 1991, 1305. (c) Streubel, R.; Ernst, L.; Jeske,
J.; Jones, P. G. J. Chem. Soc., Chem. Commun. 1995, 2113. In contrast,
only one example of an 1H-diazirine has been spectroscopically character-
ized: (d) Dubau-Assibat, N.; Baceiredo, A.; Bertrand, G. J. Am. Chem Soc.
1996, 118, 5216.
(11) To be published elsewhere.
(12) Selected spectroscopic data for 2: 31P NMR (C6D6) -123.0 (d,
1J(P-P) ) 164.3 Hz, 1J(P-W) ) 295.1 Hz, P-NiPr2), 15.0 (1J(P-P) )
164.3 Hz, σ2-P); 13C NMR (C6D6) 195.9 (dd, 1J(P-C) ) 80.6; 48.4 Hz,
PCP), 197.6 (d, 1J(P-C) ) 8.7 Hz, 1J(C-W) ) 126.9 Hz, COe), 200.2 (d,
1J(P-C) ) 33.1 Hz, 1J(C-W) ) 149.9 Hz, COa); IR (THF) 1930 (vs),
1938 (vs), 1979 (s), 2069 (s) cm-1 (νCO). For 3: 31P NMR (C6D6) -78.5
(d, 1J(P-P) ) 218.0 Hz, 1J(P-W) ) 307.8 Hz, PCl), 34.6 (1J(P-P) )
218.0 Hz, σ2-P); 13C NMR (C6D6) 189.0 (dd, 1J(P-C) ) 88.6, 34.7 Hz,
PCP), 196.7 (d, 1J(P-C) ) 8.6 Hz, 1J(C-W) ) 127.1 Hz, COe), 199.5 (d,
1J(P-C) ) 46.8 Hz, COa); IR (pentane) 1949 (vs), 1959 (vs), 2079 (s)
cm-1 (νCO). For 4: 31P NMR (C6D6) -177.5 (d, 1J(P-P) ) 148.4 Hz,
1J(P-W) ) 257.1 Hz, P-Ph), -60.0 (1J(P-P) ) 148.4 Hz, σ2-P); 1H NMR
(C6D6) 6.9-7.1 (m, 3 H, Har), 7.65 (ddd, 3J(H-H) ) 8.0 Hz, 4J(H-H) )
1.5 Hz, 3J(P-H) ) 13.2 Hz, 2 H, Har); IR (pentane) 1935 (vs), 1943 (vs),
1983 (s), 2071 (s) cm-1 (νCO). For 5: 1H NMR (CDCl3) 1.39 (d, 3J(H-H)
3
) 6.7 Hz, 6 H, CH3), 1.44 (d, J(H-H) ) 6.7 Hz, 6 H, CH3), 4.34 (sept,
3J(H-H) ) 6.7 Hz, 2 H, CHN); 13C NMR (CDCl3) 20.2 (s, CH3), 20.9 (s,
CH3), 61.0 (s, CHN), 119.7 (q, 1J(C-F) ) 318.6 Hz, CF3), 189.3 (t, J(P-
C) ) 4.3 Hz, 1J(C-W) ) 121.5 Hz, COe), 194.4 (t, J(P-C) e 1 Hz, COa),
205.1 (t, J(P-C) ) 90.9 Hz, PCP); IR (CH2Cl2) 1950 (vs), 2055 (s) cm-1
(νCO); MS (CI, CH4) m/z 498 (M+), 470 {[M - (CO)]+}, 442 {[M -
2(CO)]+}. Anal. Calcd for 5‚(GaCl4-), C12H14NO5P2WGaCl4: C, 20.31;
H, 1.99; N, 1.97. Found: C, 19.60; H, 2.39; N, 2.10.
(13) (a) King, R. B.; Wu, F.-J.; Holt, E. M. J. Am. Chem. Soc. 1988,
110, 2775. (b) King, R. B.; Wu, F.-J.; Holt, E. M. Inorg. Chem. 1988, 27,
1241. (c) Mercier, F.; Deschamps, B.; Mathey, F. J. Am. Chem Soc. 1989,
111, 9098.
S0002-7863(97)01973-2 CCC: $14.00 © 1997 American Chemical Society

9924 J. Am. Chem. Soc., Vol. 119, No. 41, 1997
Communications to the Editor
Scheme 3
Scheme 4
The definitive proof for the ionic nature of 5 arises from the
1
formation of complexes presenting identical 31P, H, and 13C
NMR data, by treatment of 3 with a slight excess of aluminium
or gallium trichloride.16 All of these complexes are highly air-
and moisture-sensitive brown oils.
The diphosphirenylium cation 5 readily reacts with 2 equiv
of diisopropylamine and 1 equiv of bis(triphenylphosphora-
nylidene)ammonium chloride (PPNCl), quantitatively affording
complexes 2 and 3, respectively. Lastly, note that 5 can be
obtained directly along with 1 equiv of diisopropylammonium
triflate, by treatment of a dichloromethane solution of 2 with 2
equiv of triflic acid at low temperature (Scheme 3).
The stability of 5 (stable for weeks in solution at room
temperature) is certainly not only due to the presence of the
metal fragment but also to the effective π-donation of the
nitrogen: the mesomeric form 5′ is likely to be the major
contributing structure (Scheme 3). Complex 5 is the first
compound featuring a phosphorus-phosphorus double bond in
a three-membered ring, and we are currently investigating the
possibility of C-functionalization of such diphosphirenylium
salts that would lead to the previously unknown 3H-diphos-
phirenes F,17 the phosphorus analogues of 3H-diazirine G
(Scheme 4).
transfer, ionization of 3 was carried out with silver triflate at
-78 °C. The dichloromethane solution immediately turned to
deep red, and after the solution was warmed to room temperature
and filtration, the 31P NMR spectrum showed only one singlet
at -157.4 ppm (no P-W or P-H coupling was observed), in
the range expected for a three-membered phosphorus hetero-
cycle.14 The presence of a W(CO)5 fragment is readily apparent
from the IR spectrum (CH2Cl2, νCO ) 1950 and 2055 cm-1).
The multiplicity of the 31P resonance can be explained either
by a symmetrical structure with 2 equiv phosphorus atoms such
as 5 or 6, or alternatively from a rapid exchange of both the
W(CO)5 fragment and the triflate group between the adjacent
phosphorus nuclei of 715 (Scheme 3). The two triplets observed
in the 13C NMR spectrum for the carbonyl groups [189.3, t,
J(P-C) ) 4.3 Hz, COe and 194.4, t, J(P-C) e 1 Hz, COa]
ruled out the rapid exchange of the metal fragment, confirmed
the η2-coordination of the heterocycle (Via the PdP bond), but
did not exclude an equilibrium between the ionic and covalent
structures 5 and 6. However, it should be noted that no
significant modification of the NMR spectra was detected on
cooling the solution to -60 °C and that the complex was only
soluble in polar solvents.
Acknowledgment. Thanks are due to the CNRS for financial
support of this work and to the Basque Government for a grant for
M.I.C.
Supporting Information Available: Listings of complete spec-
troscopic data for compounds 2-4 (2 pages). See any current masthead
page for ordering and Internet access instructions.
JA971973A
(16) The presence of the AlCl4- counterion is proved by a sharp signal
observed at 103.0 ppm in the 27Al NMR spectrum.
(14) Mathey, F. Chem. ReV. 1990, 90, 997.
(17) The formation of a transient 3H-diphosphirene has been postu-
lated: Niecke, E.; Streubel, R.; Nieger, M. Angew. Chem., Int. Ed. Engl.
1991, 30, 90.
(15) Regitz et al.3 obtained a covalent P-(trifloxy)-1H-phosphirene by
treating a P-chloro-1H-phosphirene with silver triflate.